Before he was President: James Garfield

James Abram Garfield, 1881 canal
boy
At age sixteen, Garfield ran away to work on the canal boats that
shuttled commerce between Cleveland and Pittsburgh. During his six
weeks on the boats, he fell overboard fourteen times, finally
catching such a fever that he had to return home. While recovering,
Garfield vowed to make his way in the world using brains rather than
brawn. Source

He was a preacher for about a year at a Christian church when he
decided to try his hand as principal of a high school in New York.
He didn't get that job however, so he went on to become an
instructor at the Eclectic Institute, where he was later promoted to
principal. ("Garfield," by Allan Peskin.).

Chester Alan Arthur, 1881-1885
teacher
In 1845, at the age of 15, Arthur entered Union College in
Schenectady, New York. During his school vacations, Arthur worked as
a teacher to help pay his room and board costs of $125 per year and
his college tuition of $28. Chester Arthur was nicknamed "Elegant
Arthur" for his fashion sense. He had quite a wardrobe: 80 pairs of
pants. Source

Grover Cleveland, 1885-1889 and
1893-1897 sheriff
Grover Cleveland did not feel compelled to join the Union Army
during the Civil War. Arguing that he need to stay behind and look
after his mother and sisters, he paid a substitute solider to serve
in his place. The price for substitution was $150.00.

While working in Buffalo, New York, his favorite dinner was a plate
of pickled herring, Swiss cheese, chops, and a quart of beer served
a local saloons. In 1863 Cleveland was 32 years old and received a
well paying sheriff's position in Buffalo County, where he
personally hanged two convicted murderers. He had the option to hire
someone else to do the physical work of hanging the individual
convicts, but both times chose to do the deed himself. Source